Refine
Year
Publication Type
- Conference Proceeding (141) (remove)
Has Fulltext
- no (141) (remove)
Faculty
- Physikingenieurwesen (PHY) (141) (remove)
Expertenevaluation der ergonomischen und sicherheitstechnischen Gestaltung von Krankenhausbetten
(2023)
Laser shock peening is a new and important surface treatment technique that can enhance the mechanical properties of metal materials. Normally, the nanosecond laser with pulse-width between 5 ns and 20 ns is used to induce a high-pressure shock wave that can generate plastic deformation in the top layer of metals. The femtosecond laser shock peening in the air has been studied recently, which can induce higher pressure shock wave than that of traditional nanosecond laser shock peening in a very short time. The NiTi alloy is processed by femtosecond laser shock peening, then a nanoindentation device is used to measure its surface hardness and residual stress. The hardness results of NiTi alloy before and after treatment show that the femtosecond laser shock peening can increase the hardness of NiTi alloy, which also shows that the femtosecond laser can be used to perform laser shock peening on NiTi alloy without coating.
The experiment study presents the influence of femtosecond laser shock peening (FsLSP) without a protective layer in the air on the surface hardness and surface mechanical property of NiTi shape memory alloy. Femtosecond laser shock peening is a new possibility of direct laser ablation without any protective layer under atmospheric conditions, which can produce intense shock waves with low pulse energy in the air. The average surface roughness values of the NiTi alloy samples were measured, because the surface roughness may affect its friction resistance. The results showed that the surface roughness of NiTi increased after femtosecond laser shock peening treatment. In comparison with the initial state, the coefficient of friction decreased and surface microhardness increased after femtosecond laser shock peening treatment with different FsLSP parameters. This improvement of wear properties may be attributed to the enhancement of surface microhardness and surface titanium oxide layer induced by the shock wave and laser ablation during FsLSP treatment.
In this study, we use a hybrid mode-locked external cavity diode laser with subsequent amplification and pulse compression. The system provides laser pulses of 440 fs width (assuming a sech² pulse shape) and 160 mW average output power at a repetition rate of 383.1 MHz. The laser oscillator consists of a double quantum well laser diode with a gain segment of 1080 μm length and an absorber element of 80 μm lengths. The chip’s back facet is covered with a high reflective coating, the front facet with an anti-reflective coating. The resonator itself is operated in a collimated geometry and folded by two dielectric mirrors. The used output coupler provides a transmission of 20 percent, which is coupled into a tapered amplifier. Two Faraday isolators are used to decouple the laser and the amplifier from any back reflections. Subsequently, the pulses are compressed using a single pass Martinez type pulse compressor …
Anomaly transport
(2019)
Nonlocal quantum kinetic theory and dynamical constraints on phase transitions in the early universe
(2018)